This invention relates to a zinc oxide crystal of a novel shape and a method of producing the same. Products of the present invention can be used as an industrial material and a material for the purpose of the people's livelihood.
Zinc oxide crystals obtained by gas-phase methods have various geometric shapes such as a granular shape, a needle-shape, a sheet-shape and a tetrapod-shape. Particularly, when tetrapod-like crystals are produced by such a method or under such a condition that a satisfactory controllability is not obtained, crystals other than such tetrapod-like crystals are also present in a mixed manner, and in some cases, the number of the needles is larger than the number of the tetrapod-like crystal, and these are connected together at a same junction to form the crystal. Therefore, in a group of such crystals of a complicated shape, the number of the needles is quite irregular, and hence no homogeneity is found, and the angle between the needles is not constant. Furthermore, sheet-like crystals influence the mechanism of the formation and growth of the crystal, and the crystals often are formed with such sheet-like crystals connected thereto.
As described above, there are often produced the by-product crystals in which the needles (hereinafter referred to as "legs") are interconnected at one point, and four or more legs grow randomly. There is no reproducibility in connection with the shape of such similar crystals, and they are the mixture of such a complicated shape that it is difficult to find such similar crystals of the same shape even in the same batch.
There has heretofore been proposed a mechanism of increase of the number of legs from a tetrapod-like crystal, in which new legs further grow in a twinning manner from an edge of a thin-sheet crystal formed and grown in a twinning manner between the legs of the tetrapod-like crystal. Only with such a twinning mechanism, it is difficult to control the spots of formation of such legs and the frequency of this formation, and even if the number of legs of the produced crystal, the angle between the legs of this crystal, the number of the sheet-like crystals, and the growth degree are taken into consideration, it is extremely difficult to obtain the crystal of a uniform shape.
The inventor of the present invention have made extensive study and analysis of the above crystals, having no constant shape, in various ways such as an X-ray diffraction method, an electron diffraction method and an etching treatment. As a result, it has been found that there are many factors in the growth mechanism, and that defects such as various dislocations due to the complication of these factors often develop, and it has been confirmed that no constant shape of the above crystal is due to such defects.
In several gas-phase methods of producing a zinc oxide crystal (particularly, a tetrapod-like zinc oxide crystal), the above zinc oxide crystal of a complicated shape is presented in mixed relation to a tetrapod-like crystal when metallic zinc is burned and oxidized in an atmosphere of a relatively high oxygen concentration.
Therefore, in order to obtain the totally-novel zinc oxide crystal of the present invention having a constant structure, it is necessary to establish and use a new growth method achieving a growth mechanism different from those of the conventional methods.
On the other hand, there has not yet been publicly announced or manufactured a homogeneous crystal having legs the number of which is not less than the number (four) of the legs of the tetrapod-like crystal.